The present invention relates to a process for preparing bix(oxime) monoethers of the formula I, 
where:
R1 is unsubstituted C1-C4-alkyl or C2-C4-alkenyl-, C2-C4-alkynyl- or phenyl-substituted methyl;
R2,R4 independently of one another are hydrogen or methyl;
R3,R5 independently of one another are hydrogen or C1-C4-alkyl, trifluoromethyl or phenyl.
Moreover, the invention relates to monooximes of the formula III and 
mono(oxime ethers) of the formula IV 
which are obtainable by this process. Bis(oxime) monoethers of the formula I and mono(oxime ethers) of the formula IV are interesting intermediates for preparing the fungicidal crop protection agents known from WO-A 95/21153, WO-A 95/21154 and WO-A 97/03057. 
In the prior art, the synthesis specifically of the alkenylalkyl-substituted dione derivatives I and IV has not been described (cf. WO-A 95/21153, WO-A 95/21154, WO-A 96/16030 and WO-A 97/03057). The general schemes in these publications show only synthesis routes starting from (xcex1-diketones a) or the corresponding xcex1-bis-oximes b) (see scheme 1). 
Owing to the bifunctionality, substance mixtures are to be expected as products a) in the oximation of the xcex1-diketones and b) in the alkylation of the xcex1-bisoximes. In addition to the desired monocondensation/substitution product, the unreacted and the doubly reacted product are generally also found in reactions of this type.
However, in the present case there is another more serious problem. The alkenylalkyl radical (which corresponds to R1 in scheme 1) is much more sterically demanding than the methyl radical (Rxe2x80x3). Any monocondensation/substitution product formed would presumably have the wrong regio- and stereochemistry (cf. Liebigs Ann. Chem. (1974) 1908-1914). The sequence shown in scheme 1 is therefore unsuitable for synthesizing bis(oxime) monoethers of the formula I.
It is an object of the present invention to provide a process which allows the targeted synthesis of compounds of the formulae I and IV.
We have found that this object is achieved by the process mentioned at the outset, which comprises
a) treating an acetoacetic ester of the formula II 
with a nitrite initially under alkaline conditions and subsequently under acid conditions and
b) alkylating the resulting monooxime III 
in the presence of a base to give the mono(oxime ether) IV 
and finally
c) reacting the mono(oxime ether) IV with hydroxylamine or its acid addition salt to give the bis(oxime) monoether I.
The process according to the invention is illustrated using the synthesis of hex-5-ene-2,3-dione 3-(O-methyloxime) 2-oxime as an example (see scheme 2). 
The individual steps of the process according to the invention are illustrated in more detail below.
Step a):
Step a) is carried out using the method of the procedure described in U.S. Pat. No. 4,707,484.
Alcohols, such as, for example, methanol, and in particular water may serve as solvent. In certain cases it may be advantageous to add solubilizers, such as, for example, surfactants or ethylene glycol.
Suitable bases are, in particular, sodium hydroxide and potassium hydroxide, which are usually employed in equimolar amounts or in an up to ten-fold molar excess, based on the acetoacetic ester II.
Nitrite is to be understood as, for example, an alkali metal nitrite, in particular sodium nitrite, which is usually employed in equimolar amounts or in an excess of up to 30 mol %, based on the acetoacetic ester II.
In general, the reaction temperature should not exceed 40xc2x0 C. since otherwise undesirable side reactions occur. In water, the reaction is therefore preferably carried out at from xe2x88x9220 to 40xc2x0 C., in particular at from 0 to 15xc2x0 C.
After a period of from 10 to 48 hours, the reaction mixture usually becomes clear. A pH of from 0 to 5 and preferably of from 1 to 3 is then established using an acid, such as, for example, hydrochloric acid or sulfuric acid.
Work-up is carried out by customary methods, for example by extraction. For purification, the oxime can, for example, be converted into the corresponding salt using bases and precipitated again using an acid.
The acetoacetic ester II employed for the reaction can be prepared as described in Tetrahedron (1985) 4633 (see scheme 3). 
The alkenylalkyl compounds of the formula A in which R2 to R5 are as defined in claim 1 and L1 is halogen, acyloxy, alkylsulfonyloxy or arylsulfonyloxy are known or can be synthesized by processes known from the literature (Z. Org. Khim. (1997) 486; Bull. Chem. Soc. Jpn. (1980) 2586; J. Am. Chem. Soc. (1984) 2211; J. Am. Chem. Soc. (1960) 1886; DE-A 19 556 66; DE-A 33 173 56; EP-A 271212; Tetrahedron Let. (1986) 6027; Tetrahedron Let. (1994) 1371 and 2679; J. Fluorine Chem. (1997) 67; Helv. Chim. Acta (1951) 1514; Organomnet. Chem. (1985) 395).
Step b):
The alkylation is usually carried out in the presence of an inert organic solvent. Suitable solvents are, inter alia, aliphatic or aromatic hydrocarbons, such as, for example, toluene, xylene, heptane or cyclohexane, aliphatic or cyclic ethers, such as, for example, 1,2-dimethoxyethane, tetrahydrofuran or dioxane. Preference is given to using polar aprotic solvents: ketones, such as, for example, acetone, nitriles, such as, for example, acetonitrile, amides, such as, for example, dimethylformamide, dimethylacetamide or N-methylpyrrolidone, or ureas, such as tetramethyl urea.
The alkylating agent used is usually a halide, preferably a chloride or bromide, a sulfate, preferably dimethyl sulfate, a sulfonate, preferably a methanesulfonate (mesylate) or a toluene sulfonate (tosylate).
The amount of base or alkylating agent is preferably from one to two times the equimolar amount, based on the compound III.
In general, the reaction is carried out in the presence of an inorganic base, such as sodium hydroxide or potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate, or of an alkali metal alkoxide, such as sodium methoxide or potassium tert-butoxide.
The reaction temperature is generally at from 0xc2x0 C. to 50xc2x0 C., preferably from 0xc2x0 C. to 40xc2x0 C. and in particular at room temperature.
Work-up can be carried out, for example, by extraction.
To remove residual amounts of alkylating agent, it may be advantageous to wash the reaction batch with, for example, ammoniacal solution.
Step c):
Hydroxylamine is employed either in the form of an acid addition salt or as free base, it being possible to liberate the latter from the salt by addition of a strong base.
Preference is given to using the acid addition salts of the hydroxylamine. All customary acids are suitable for preparing the acid addition salts. Just a few of them are listed below, by way of example: carboxylic acids, such as acetic acid or propionic acid, dicarboxylic acids, such as oxalic acid or succinic acid, mineral acids, such as phosphoric acid or carbonic acid and in particular hydrochloric acid or sulfuric acid.
If the acid addition salts of the hydroxylamine are employed, it is generally advantageous to add a base to bind the acid liberated in the reaction. In many cases, a pH of from 3 to 7 and in particular of from 4 to 6 has been found to be advantageous for the oximation. Outside these pH ranges, side reactions such as ring closure reactions may occur.
In general, 1 to 2.5 molar equivalents of a base are added.
Suitable bases are, in particular, pyridines, trialkylamines, sodium hydroxide, sodium acetate and sodium methoxide. If sodium acetate is employed, it is customary to add glacial acetic acid.
Conversely, it is of course also possible to employ the hydroxylamine as free base and to use one of the abovementioned acids to establish the abovementioned pH range.
Solvents which can be employed are, for example, those described in the previous step. Other suitable solvents are carboxylic acids, such as acetic acid, or else water/pyridine mixtures. Alcohols, such as methanol, ethanol, n-propanol or isopropanol, and mixtures of these with water and/or pyridine are particularly suitable.
The reaction temperature is generally from xe2x88x9220 to 100xc2x0 C., preferably from 0 to 40xc2x0 C. and in particular from 20 to 25xc2x0 C.
Work-up of the reaction mixture is preferably carried out by extraction, as described in the previous step. To remove the base completely, it may be advantageous to wash the crude product first, with a dilute aqueous acid and then with water.
The process according to the invention allows the preparation of, in particular, monooximes of the formula III, 
mono(oxime ethers) of the formula IV 
and bis(oxime) monoethers of the formula I,
where: 
R1 is unsubstituted C1-C4-alkyl or C2-C4-alkenyl-, C2-C4-alkynyl- or phenyl-substituted methyl;
R2,R4 independently of one another are hydrogen or methyl;
R3,R5 independently of one another are hydrogen or C1-C4-alkyl, trifluoromethyl or phenyl.
As illustrated by the compounds I in Scheme 4, the above formulae can also be represented in a different, conformeric notation. 
In the above definitions of the compounds I, II, III, IV and A, collective terms were used for the radicals R1 to R5 which represent individual enumerations of the individual group members. The radicals alkyl, alkenyl or alkynyl can be straight-chain or branched.
Examples of other meanings are:
halogen: fluorine, chlorine, bromine or iodine;
C1-C4-alkyl: methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl and 1,1-dimethylethyl;
C2-C4-alkenyl: ethenyl, prop-1-en-1-yl, prop-2-en-1-yl, 1-methylethenyl, but-1-en-1-yl, but-2-en-1-yl, but-3-en-1-yl, 1-methyl-prop-1-en-1-yl, 2-methyl-prop-1-en-1-yl, 1-methyl-prop-2-en-1-yl and 2-methyl-prop-2-en-1-yl;
C2-C4-alkynyl: ethinyl, 1-propinyl, 2-propinyl, 1-butinyl, 2-butinyl, 3-butinyl, 1-methyl-2-propinyl.
With respect to their suitability for use as intermediates for preparing the crop protection agents disclosed in WO-A 95/21153, WO-A 95/21154 and WO-A 97/03057, particular preference is given to the compounds of the formulae I, III and IV with the following substituents, where the preference applies in each case on its own or in combination:
R1 is methyl, ethyl, benzyl or propargyl and in particular methyl or ethyl;
R2,R4 independently of one another are hydrogen or methyl;
R3,R5 independently of one another are hydrogen, methyl or trifluoromethyl.